Did you know that NASA has a department to make sure that spacecraft are clear of microbes and other nasties?  After all we wouldn’t want to introduce earth cooties on an unsuspecting alien planet.  On the flip side we won’t want alien nasties coming to earth.  I totally believe this could happen.  Spider-Man had extraterrestrial symbiotes come back to earth with him.  The Andromeda Strain had an alien virus.  Star Wars had mynocks chewing on the power cables.   If Spider-Man and Han-Solo can’t keep extraterrestrial hitchhikers away what chance do we have?

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